ipcs

The ipcs command shows the size of each shared memory segment for the SGA. If there is not enough memory for the entire SGA to fit in a contiguous piece of memory, the SGA will be built in non-contiguous memory segments. In the event of an instance crash, there is possibility that the memory will not be released.

# ipcs -b

It is usually preferable to have the entire SGA fit into a single shared memory segment because of the overhead that can be required to track more than one segment and the time required to switch back and forth between those segments.

If the SGA doesn't fit into a single contiguous piece of memory, consider decreasing the size of SGA.

Thanks